According to a source inside Microsoft, over 25 percent of Vista installations in the US at the end of last year were 64-bit. There were several major drivers for the switch to 64-bit, most related to cheap DDR2 DRAM.

Jon DeVaan, Senior Vice-President of the Windows Core Operating System Division, agrees. "From our point of view we believe that we have accomplished the tipping point in terms of 64-bit adoption. Now, this happened to a large degree because memory prices are coming down, and another dynamic that we've seen in the United States is that the retail channel is looking to use RAM upgrades as a way to boost margin. So what that means is that 64-bit machine run rate is increasing rapidly, and that means our ability to support those 64-bit machines fully in the broad ecosystem is a really important thing."

Any PC with 4GB of RAM or more must use a 64-bit installation of Windows in order to address the full amount of RAM. Typically a 32-bit installation would recognize a maximum of 3-3.5GB of RAM.

Instead of purchasing a 32-bit version and then having to change to 64-bit later when they purchase more RAM, many are choosing 64-bit at the start. Over 75 percent of Windows sales are based on OEM installations of new computers.

The majority of Core i7 platforms are also using 64-bit operating systems, due to the triple channel memory setup using more RAM.

With the switch to Windows 7, it would be easiest for PC OEMs to adopt 64-bit exclusively. That would reduce the number of SKUs (Stock Keeping Units) and drivers that would be needed by half, not an insignificant number when you consider that Windows 7 will ship in at least 4 editions. Multiply that by at least 34 localized language versions.

"Put more simply, usage of 64-bit Windows Vista is growing much more rapidly than 32-bit. Based on current trends, this growth will accelerate as the retail channel shifts to supplying a rapidly increasing assortment of 64-bit desktops and laptops," said Chris Flores, a Director on the Windows Client Communications Team.

Since 64-bit Vista and Windows 7 can run 32-bit applications, the last remaining hurdle is driver compatibility. Many new devices now have 64-bit device drivers available for Vista, and those should be mostly compatible with Windows 7.

An important tool is the Windows Vista Compatibility Center. Devann thinks that 64-bit support will drive sales: "They can go here and look at 64-bit compatibility, and with the trend that we just saw this is a good place for communicating with your customers about your support for 64-bit, so that they can prefer your product if they have one of these 64-bit systems".

Devann addressed the crowd at WinHEC with the following message, "I urge everyone here to make sure that you have the right 64-bit support, and in general 32-bit software runs fine on 64-bit Windows, but when it comes to drivers, that's where the work is. And with this audience, it's something that we're all acutely aware."

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